This invention relates generally to a composite construction engineering material consisting of structural reinforcing elements of discontinuous, non-fibrous configuration, i.e., three-dimensional structural reinforcing elements rather than slender, threadlike structures (or combinations of threadlike structures). This composite construction engineering material can be constructed to possess enhanced engineering properties, as well as improved index properties, as compared to the unreinforced matrix material. This invention relates also to elements of a composite construction engineering material, with improved characteristics. It further relates to methods to incorporate these special structural reinforcing elements into an artificial construction material or to form an essentially artificial construction material.
The projected primary application of this invention relates to the improvement, reinforcement, enhancement, and/or stabilization of soil or soil-like materials in geotechnical engineering applications. However, additional applications include, but are not necessarily limited to, the improvement, reinforcement, enhancement, and/or stabilization of other construction materials such as, but not limited to, Portland cement, concrete, asphalt, lime, stone, slag, or any mixture or combination of these materials with or without soil. Because the potential applications within the construction industry appear to be numerous, a complete discussion of all these applications is not practicable. Therefore, the discussion related to the incorporation of non-fibrous, discontinuous, structural reinforcing elements within construction engineering materials will be limited to geotechnical engineering applications using soil or stone as the matrix material. The discussion, however, applies in a general sense (and in a specific sense, where appropriate) to the incorporation of these elements within any construction engineering material.
In the construction industry, both in building foundation construction and on-grade construction, including slabs and pavement systems, as well as earthwork projects such as dams, levees, embankments, fills and retaining walls, the engineering and index properties of soils significantly influence the end product. The characteristics of the soil which are usually the most influential, include the shear strength of the soil, the consolidation or compression characteristics of the soil, the compactibility of the soil, the density of the soil, and the permeability of the soil. These characteristics influence the bearing capacity of foundations, the settlement of structures, the lateral earth pressure against retaining walls, the performance and useful life of slabs and pavements, the drainage characteristics of subsoils, and the slopes of embankments.
The present invention improves these characteristics by producing a composite (reinforced) geotechnical engineering material or an artificial soil material, which can increase the strength, decrease the compressibility, increase the ductility, increase the permeability, decrease the weight, and increase the constructibility (compactibility) in comparison with unreinforced soil. These improvements can be achieved without the use of continuous reinforcement elements (commonly called geotextiles or geofabrics) or without the use of additive fibers.
Soil reinforcement in the form of stabilizing or improving soil characteristics for construction purposes is not a new concept. Chemical stabilization by introducing hydrated lime or quicklime into a soil was utilized two thousand years ago. Introduction of sticks, tree parts, or straw to soils to improve soil properties was practiced by ancient peoples on a number of continents. However, manufactured products introduced into a soil matrix to enhance its properties are a relatively recent innovation. The impetus to this industry was provided by the introduction of flat, thin strips of reinforcing materials to a soil backfill. The strips were constructed of galvanized steel, and later synthetic materials such as polypropylene have been used. These strips were placed horizontally between lifts of soil backfill. The most common use of the invention was to improve retaining wall design and performance.
Subsequently, the use of woven and non-woven fabrics and thermoplastic grids has been developed. These materials, often called geotextiles or geofabrics, are generally constructed of thermoplastics or polyesters. They are utilized as continuous sheets, normally placed horizontally or near horizontally between lifts of soil. The primary purposes of these reinforcing sheets are to improve the bearing capacity of the soil and to reduce lateral soil pressures against retaining walls or to increase stability within sloped embankments.
More recently, there has been some activity involving the introduction of non-continuous, discrete fibers into soil matrixes. This basic technique began with the reinforcement of concrete to improve various characteristics of the concrete, including tensile strength, ductility and crack resistance. Fiber materials used include steel fibers and polypropylene fibers. Fibers have been subsequently introduced into soils on a limited scale. Research has been documented since 1980, on the introduction of natural and synthetic fibers into a soil matrix for the purpose of improving the composite material's engineering properties, mainly its shear strength and stress-strain response.
An example of the introduction of fiber elements into the soil to enhance the properties of the composite soil mixture has been described in U.S. Pat. No. 4,790,691. This patent discloses the use of additive fibers varying from 0.1 to 5 percent by weight to that of the soil matrix. The single method disclosed for constructing the composite mixture is to mix the fiber additives together with the soil to form a blend. Constructing an improved composite geotechnical engineering material or an artificial soil consisting of discontinuous structural reinforcing elements of a non-fibrous configuration appears not to have been attempted heretofore. Methods of mixing which include both blending the discontinuous reinforcing elements with the soil, and also placing these elements in layers between soil lifts, has not been previously attempted. Use of synthetic, non-fibrous reinforcing elements by themselves as an artificial soil likewise appears not to have been previously attempted.